FR2673177A1 - SINK BODY WITH A POROUS ZONE, IN PARTICULAR SILICON CARBIDE, FOR A MECHANICAL TRIM AND TRIM COMPRISING SUCH A SINTERED BODY. - Google Patents

Abstract

The invention relates to a sintered body, in particular made of silicon carbide, which can be used as a friction part. According to the invention, the sintered body is characterized in that it comprises a first zone made of a first porous ceramic material and a second zone made of a second non-porous ceramic material. The sintered body of the invention can be used in mechanical seals.

Description

SINTERED BODY WITH POROUS ZONE, IN PARTICULAR SILICON CARBIDE,

  FOR MECHANICAL TRIM AND TRIM COMPRISING SUCH A SINTERED BODY

  The present invention relates to a sintered body, comprising a porous zone, in particular silicon carbide, for a mechanical seal and a lining comprising such a sintered body. Mechanical seals are well known assemblies comprising two slip rings on top of one another to make

  rotating pump shaft seal on self-propelled motors

mobile for example.

  For these fittings, more and more rings of ceramic materials are used, for example carbide

  sintered silicon for a ring and carbon-based material, in particular

  graphite, for the counter-ring.

  It has recently been advocated to use in these fillings

porous ceramic materials.

  However, the presence of pores within these materials causes a decrease in their mechanical strength and their

thermal conductivity.

  The main object of the invention is the development of a ceramic material that can be used in friction, in particular in a mechanical seal and having improved mechanical strength and thermal conductivity compared to those of porous materials. Another object of the invention is to provide a material which, while having improved mechanical strength and thermal conductivity, reduces the wear of the counter ring, while

  especially for high rotation speeds.

  For this purpose, the sintered body according to the invention is characterized

  in that it comprises a first zone made of a first porous ceramic material and a second zone made of a second ceramic material

non-porous.

  The sintered body according to the invention has a high mechanical strength which results in a breaking stress which can

  to be of the order of twice that of the porous material.

  In addition, it has been found after long-term tests (1000 hours) and for high rotational speeds (higher than

  6000 rpm) a very good seal of the linings used

  sintered bodies of the invention.

  Other features and details of the invention are

  will be clearer when reading the description that goes

  follow with reference to the accompanying figures for which: Figure 1 is a photograph taken under an electron microscope of a body according to the invention showing the entire porous zone thereof, Figure 2 is a photograph of the same type but to the interface

  between the porous zone and the non-porous zone.

  With regard first of all to the nature of the above-mentioned ceramic materials, it will be noted that the first material forming the first zone and the second forming the second zone may be

identical or different.

  When using different materials, it is preferable that these materials obey sintering conditions

that are compatible.

  According to a particular embodiment of the invention,

  uses the same material for the first and second area.

  Different types of ceramics can be used.

  Mention may be made of materials based on alumina, zirconia, aluminezircone, aluminum nitride (Al N), boron carbide

B 4 C.

  However, according to a preferred embodiment of the invention,

  Silicon nitride (Si 3 N 4) and silicon carbide (Si C) can be mentioned for the latter. Si C a or Si C i can be used, or combinations of these two polytypes can be used.

any proportions.

  The ceramic materials of each of the zones may furthermore comprise all the usual and well-known sintering additives, for example carbon, boron, or aluminum for SiC, yttrium oxide, spinel and the like. alumina for Si 3 N 4, yttrium oxide for Al N, or also stabilizers of zirconia such as yttrium, magnesium, calcium or cerium oxide.

  The invention also applies to sintered bodies in the

  which the aforementioned materials may be of the composite type, that is to say based on several phases and in particular based on carbon

  free in particular in graphite form and / or boron nitride.

  Thus, there may be mentioned Si C / C, Si 3 N 4 / BN and Al N / BN composites.

A 1203 / BN.

  It is possible, in particular, to envisage composites based on SiC and comprising up to 48% by weight of free carbon, especially up to% and more particularly up to 10%, this carbon possibly being in the form of a carbon mixture. amorphous graphite carbon

in any proportions.

  Composite type bodies comprising graphite as well as those comprising boron nitride are particularly interesting.

  because they have improved lubricating properties by reducing the coefficient of friction. Finally, the ceramic materials used in the context of

  the invention has a grain size which is generally between 0.5 and 500 m, preferably between 0.5 and 20 j m.

  According to an essential characteristic of the invention, the sintered body comprises a first part or zone which is porous and

  another part or second zone that has no porosity.

  According to a preferred embodiment, this first porous portion constitutes a surface zone on the surface of the second zone. The porous zone preferably has a thickness of at least 20 μm, more particularly at least 50 μm, and in particular

between 100 and 1000 J m.

  Another important feature is the total porosity of the material of the first zone.

  This porosity can be very important insofar as the sintered body furthermore comprises a non-porous part on which the porous part rests. However, it is preferable that this porosity does not exceed 50%, more particularly it is at most

  18%, it is in this case that a maximum seal is obtained.

  On the other hand, this porosity is at least 4%.

  By total porosity is meant that obtained by taking into account the open and closed pores. In the particular case of composites, this porosity (P), expressed in%, is given by the formula: P = 100 x + 100-x ld 2 d 1 L in which d 1 is the density of the majority phase (for example Si C or Si 3 N 4) of the composite, d 2 the density of the minority phase (for example C or BN), d the density of the body and x the mass percentage of the minority phase present

in the body.

  In the particular case of a composite Si C / C, this formula would be:

P = 100 {d x + -

L 2.25 3.21

  d being as defined above and x being the mass percentage of free carbon contained in the material; 2.25 being the density of the free carbon and 3.21 that of the silicon carbide. Moreover, the porous material forming the first zone of the sintered body may have pores whose mean diameter may

  vary in a wide range usually from 10 to 500 μm.

  This average diameter is that obtained on the basis of values

  measured by scanning electron microscope examination.

  The pores of the body according to the invention are in a spherical shape or in a form close to the sphere. This shape makes it possible to achieve high porosities by sealing

total body.

  On the other hand, these pores are essentially closed pores. Regarding moreover the material constituting the second non-porous zone, it preferably has a density as high as possible. The material preferably has a porosity.

total less than 4%.

  Finally, a characteristic of the body of the invention lies in the perfect continuity that exists between the two zones, especially in the case where these two zones consist of the

same material.

  One can thus observe a total absence of cracks between the zones, one can not distinguish a discontinuity between these.

  This appears clearly in the picture of Figure 2.

  More particular embodiments will be described. It should be noted that these embodiments can be applied to the various types of materials mentioned above but according to a preferred variant, the material used is Si C. According to a particular embodiment of the sintered body of the invention, the first material has an average pore diameter

between 40 and 200 iim.

  It has been found that for an average pore diameter of less than

  at 40 pm, a higher wear was observed at least on the counter-seal of the mechanical seal, particularly when it is

in graphite.

  Moreover, it is below an average diameter of 200 μm that the mechanical strength of the first zone of the sintered body is optimal. It may also be advantageous to have an average diameter of

  pores of at least 50 μm, and more particularly at least 601 μm.

  Thus, according to different variants of the invention, it will be possible to envisage sintered bodies having an average pore diameter

  between 50 and 200 μm, and more particularly 60 and 200 μm.

  According to another still more particular embodiment of the sintered body of the invention, the material may have a maximum value of the pore diameter of 150 μm, and more particularly a

  value which lies in the range 40 150 ym.

  It may be advantageous to have a pore diameter of between 50 and 150 μm, and more especially 60 and 150 μm, and even more

  more particularly 60 and 100 lm.

  Finally, the porosity may vary within the range of 50 to 4% indicated above, but preferably the first material has a porosity of between 4 and 18%, especially between 5 and 15%, and

more particularly 8 and 15%.

  The process for preparing the sintered bodies according to the invention

will now be described.

  As regards the material for the porous zone, this can be obtained by a process which consists of adding a pore-forming agent in the form of microbeads or granules to the mixture

  products for the preparation of the sintered material.

  The porogenic agent may be used in several ways. For example, a slip may be formed in a ball mill based on the starting ceramic material, sintering additives and a binder in water or in an organic solvent to this slip, is then added with stirring

  The pore-forming agent is finally dried by atomization.

  Another way is to form and then to dry a slip of the type described above, but without the pore forming agent Au

  dry product thus obtained, this agent is then dry blended.

  The porogenic agents that can be used are well known. They are generally organic products of the polymer type. Products obtained from an emulsion polymerization are preferably used. These products must not be soluble in the water or the organic solvent used in the composition. of the slip They

  must also be able to withstand

in particular.

  An example of this is polystyrene, polymetha-

methyl crylate, polyamide.

  The dense material is prepared in a well-known manner by forming a slip of the same type as that described above,

of course without pore-forming agent.

  A subsequent step in the process is shaping.

  This shaping can be done by isostatic pressing

  or uniaxial dry products obtained previously.

  This pressing takes place in a manner known per se.

  For example, in the case of uniaxial pressing, it is possible to initially fill the pressing mold with a first layer of dry product containing the porogen, and then secondly to dispose on this first layer a certain amount of

dry product free of porogen.

  Another method of shaping can be used by casting a first slip comprising porogen in a plaster mold, then in a second time by casting in the same mold

a porogen-free slip.

  After formatting, we get a raw part and a

  In known manner, this green part is heat treated in order to eliminate

  binders and the blowing agent and, in the case of Si C, pyrolysis

  be the precursor of the sintering additive carbon.

  The part is then sintered in a manner known per se.

  The sintering temperature depends on the material and is generally between 1400 and 25000 C. The process is carried out according to the nature of the

  material under vacuum or under nitrogen or neutral gas.

  The invention also relates to mechanical seals comprising a fixed ring and a rotary ring of which at least one is

  consisting of the sintered body as just described above.

  The other ring may be made of a material based on carbon and in particular carbon impregnated with resin This material may also be silicon carbide or silicon nitride; it can also be a sintered alumina body This can still be a

  metallic type material for example carbon steel.

  Finally, it is possible to implement a filling in which

  the two rings would consist of the sintered body according to the invention

tion.

  The sintered body of the invention can also be used in bearings.

  Of course, the sintered body of the invention can be

  used in other applications than mechanical seals.

  Thus, it can be used in any friction system of the type for example abutment, bearing or slide having at least one friction piece formed by said body or a part of which is constituted of said body can thus be used for example in bearings and in the following configurations: bore in sintered body metal shaft, bore in sintered body shaft in sintered body, bore in sintered body metal shaft with liner

sintered body or graphite.

  An example will now be given.

EXAMPLE

  Preparation of the trays A first 60% solids content slurry is formed in water comprising 1% boron, a phenolic resin supplying 1.5% of carbon after pyrolysis and 3% of polyethylene glycol. This first slip contains as its of 6% by weight relative to the Si C of PLEXIGUM M 914 (polymethyl methacrylate) of average

grains of 90 pm.

  The porogen was mixed with the slip with stirring.

  A second slip is prepared identical to the first,

but without pore-forming agent.

  The slips are then separately dried and

spray granulated.

  A first layer of dry product containing pore-forming agent is introduced into a pressing mold, then a second layer of dry product without porogen is then pressed at 1500 bar to obtain

a raw room.

  After a thermal treatment under nitrogen up to 600 C which allows in particular the removal of the porogen and the pyrolysis of the phenolic resin, the part is then sintered at 2070 C under argon

for 1 hour.

  A ring with an internal diameter of 19 mm and an external diameter of 28 mm is obtained, its total thickness is 3.5 mm. The porous zone is 0.78 mm thick and its total porosity is 13%. With regard to the porous zone, the total porosity of the material constituting it is 2.5%. Tests The ring is tested after the running surface of the friction surface has been ground as a rotating slip ring in a mechanical seal.

  fixed slip counter-ring is made of graphite carbon.

  The conditions of the test are the following temperature: 1300 C fluid: pure antifreeze

rotation speed: 6700 rpm.

Pressure: 1 bar

Duration of the test: 1000 hours.

  After the test, the corrugations on the counter-ring are measured, these are very weak, ie they have a

height of not more than 0, lim.

  After a static sealing test at 20 bar, the ring

  is waterproof, which shows that the porosity is fully closed.

  In addition, mechanical flexural tests are carried out 3

  20 C points on 25 x 5 x 3 mm test pieces.

  The test piece E1 consists of a sintered body according to the invention. This body comprises a porous zone of 700 .mu.m in thickness, the total porosity of which is 13% and the average pore diameter of .mu.m.

  The test piece E 2 consists of a whole sintered body

  The two bodies were prepared in a manner similar to that described for the preparation of the rings, it being understood that only the slurry with the same characteristics as those given above for the porous zone of the E 1 test piece.

  blowing agent was used to make E 2.

  In the case of the test piece El, the compressed zone, during the

test, is the porous area.

The following results are obtained:

EJ E 2

  average breaking stress of (M Pa) 446 213 Weibull module m 17 20

Claims (12)

  Sintered body characterized in that it comprises a first zone made of a first porous ceramic material and a second zone in one   second non-porous ceramic material.   Sintered body according to Claim 1, characterized in that the abovementioned ceramic materials are based on at least one element chosen from alumina, zirconia, zirconia alumina and nitride. of aluminum, boron carbide.   Sintered body according to Claim 1, characterized in that the abovementioned ceramic materials are based on at least one element   selected from silicon carbide and silicon nitride.   Sintered body according to Claim 2 or 3, characterized in that the abovementioned ceramic materials are additionally based on carbon,   in particular graphite and / or boron nitride.   Sintered body according to one of the preceding claims,   characterized in that the first and second aforementioned materials are identical.   Sintered body according to one of the preceding claims, characterized   characterized in that the first area mentioned above is a surface area- the.   Sintered body according to one of the preceding claims, characterized   characterized in that the first aforementioned zone has a thickness of at least 20 m, more particularly at least 50 pm, and in particular between 100 and 1000 pm.   Sintered body according to one of the preceding claims, characterized   characterized in that the first ceramic material has a porosity   total of not more than 50%, more particularly not more than 18%.   Sintered body according to one of the preceding claims, characterized   characterized in that the first ceramic material has pores   whose average diameter is between 10 and 500 gm.   Sintered body according to one of the preceding claims, characterized   characterized in that the first material has pores whose   average diameter is between 40 and 200 gm.   Sintered body according to claim 10, characterized in that the first material has an average pore diameter of 50   and 200 μm, and more particularly between 60 and 150 μm.   Sintered body according to claim 10 or 11, characterized in that the first material has a porosity of between 4 and 18%, especially between 5 and 15%, and more particularly between 8 and%. 13 Mechanical seal with fixed ring and ring   rotary device, characterized in that at least one of the rings is constituted   of the sintered body according to one of claims 1 to 11.   14 Stop-type, bearing or slide system comprising at least one friction part constituted by a body according to one of the   claims 1 to 11 o a part of which is constituted of said body.